Heads up fellow embedded developers!
In order to provide a solid and stable foundation for embedded development with Rust 2018, a change has landed in Rust earlier today (https://github.com/rust-lang/rust/pull/53648) which will potentially break your builds. It should materialise in the next nightly Rust build.
You can read the details about this change and the required tweaks to fix your build here: https://rust-embedded.github.io/blog/2018-08-2x-psa-cortex-m-breakage/
Sorry for the inconvenience.